The following was written by Alan Rockoff, MD and medical author.

Some men never go "bald" but everyone's hair thins out over the years. The term "androgenetic" refers to the fact that common balding requires both male hormones (androgens) and a genetic tendency to lose hair. Because there are many genes involved, however, you can't look at 
your parents and know how much hair you will lose or how fast you will lose it. In particular, the idea that hair loss is passed down from the mother's side of the family is folklore, not fact.

The problem of hair loss has resulted in many other myths and misconceptions. For instance, wearing hats does not "choke off" hair roots and promote baldness. Likewise, longer hair does not put a strain on roots.

Once you think your hair is thinning, it's worth a check to be sure. Even men
who never lose much hair develop some receding at both temples during adolescence. Boys' hairlines are straight across; adult men have more of an M shape.Many conditioners, shampoos, vitamins, and other products, as well as 
procedures involving lasers and heat, claim to help hair grow in unspecified ways. These are harmless but useless and not worth the investment. 

What causes hair loss?
There are many causes of hair loss on the scalp. In general, most hair loss is 
not associated with systemic or internal disease, nor is poor diet a frequent factor. Thyroid disease can cause hair loss, but thyroid tests on people who have ordinary hair loss are usually normal. 

Although many medications list "hair loss" among their potential side effects, drugs are also not overall common causes of thinning or lost hair. On the other hand, with cancer treatments and immune suppression medications, hair loss is not uncommon.

One useful way to classify hair loss is by whether the loss is localized and 
patchy, or whether it affects large areas or the whole scalp.

Patchy hair loss - 
Some conditions produce small areas of hair loss, while others affect large areas of the scalp. Common causes of patchy hair loss are:

  • alopecia areata (patches of baldness that usually grow back)

  • traction alopecia (thinning from tight braids or ponytails)

  • trichotillomania (the habit of twisting or pulling hair out)

  • tinea capitis (fungal infection)

Alopecia areata
A common condition, alopecia areata usually starts as a single, quarter-sizedcircle of perfectly smooth baldness. Alopecia patches usually regrow in three to six months without treatment. Sometimes, hair 
grows back in white. In another variant, alopecia can produce two or three bald patches. When these 
grow back, they may be replaced by others. The most extensive form is called 
alopecia totalis, in which the entire scalp goes bald. It's important to emphasize that patients who have localized hair loss 
generally don't go on to lose hair all over the scalp. Alopecia can affect hair 
on other parts of the body too-- for example, the beard.

Alopecia areata is considered an autoimmune condition, in which the body 
attacks itself (in this case its own hair follicles). Most alopecia patients, however, do not have systemic problems and need no medical tests. Alopecia is also often blamed on "stress," but in fact it's usually the other way around: 
Having alopecia causes the stress, at least until people find out what it is.

Treatments for alopecia areata include injecting steroids into affected patches 
to stimulate hair growth. This is not practical for large areas. Other treatments, such as oral steroids or ultraviolet light therapy, are either toxic or impractical. In most mild cases, patients can comb over the affected areas. In more severe and chronic cases, some patients wear hairpieces; nowadays some men shave their whole scalp, now that this look has become fashionable.

Traction alopecia
Tight braids and ponytails can pull hard enough on hairs to make them fall out. If this happens, it's best to choose hairstyles that put less pressure on hair roots. The sooner this is done the better, to 
avoid permanent damage.

This melodramatic name refers to the habit of pulling at hairs or twisting 
them, sometimes without realizing it. The scalp and eyelashes are often affected. Unlike alopecia areata patches, which are perfectly smooth, hair patches in trichotillomania show broken-off hairs. Treatment is entirely behavioral: You have to notice that you're doing it and then stop!

Tinea capitis (fungal infection)
Fungal infection of the scalp for the most part affects school-age children. Bald spots usually show broken-off hairs. Oral antibiotics are needed to penetrate the hair roots and cure the infection, after which hair grows back.  

Generalized (diffuse) hair loss  

Common conditions in this category are:
" telogen effluvium (rapid shedding after fever or sudden weight loss)
" androgenetic hair loss ("male-pattern baldness," "female-pattern baldness")

Telogen effluvium
Under normal conditions, scalp hairs live for about three years (the anagen, or
growing, phase); they then enter the telogen, or resting, phase. During this three-month period, the hair root shrivels up into a small white "club," then the hair falls out. It is therefore normal to lose about 100 hairs every day, more of them on days when shampooing loosens the hairs that are ready to fall out. The hairs are then replaced by the body.

Sometimes people worried about losing their hair start noticing hairs on their 
pillow or in the sink, not realizing that they've always been there. A close look at these will usually reveal the white "club" at the end, showing that these hairs were already dead. Normally, about 10% of scalp hairs are in the telogen phase.

There are several circumstances that produce a "shock to the system" that alters the hair growth rhythm. As a result, as much as 30-40% of the hairs can cycle into telogen. Three months later hairs come out in a massive hedding (effluvium), especially near the front of the scalp. These include:

  • high fever

  • sudden weight loss (crash dieting)

  • surgery

None of these has to be life-threatening, nor does hair loss always follow 
them. (It can happen after one pregnancy but not the next.) But when the hair falls out, it's all over the place--covering the pillow, clogging the drain, and so forth. Paradoxically, the more dramatic the hair loss, the better the prognosis,because when the body gets back into normal rhythm, most if not all of that hair comes back. No special treatment is needed. Normal shampooing can continue, because this only loosens hairs that were going to come out anyway.

Androgenetic alopecia ("male-pattern baldness," "female-pattern baldness")
Everyone loses hair, but men do it better--faster, earlier, and more extensively.Doctors refer to common baldness as "androegentic alopecia," which implies that a combination of hormones and heredity (genetics) is needed to develop the condition. (The male hormones involved are present in both men and women.)

Male-pattern baldness
Even men who never "go bald" thin out over the years. Unlike those with 
reversible telogen shedding, those with common male-pattern hair loss don't notice much hair coming out; they just see that it's not there anymore. Adolescent boys notice some receding near the temples as their hairlines change from the straight-across boys' pattern to the more "M-shaped" pattern of adult men. This normal development does not mean they are losing hair.

Some "myths" about male-pattern baldness:

You inherit baldness through your mother's male relatives.

-Actually, baldness can come from either side of the family, or both. Looking at your family can give you at best an educated guess about how you'll turn out.

Longer hair puts a strain on roots.

-They don't. And hats don't choke off the circulation to the scalp to cause hair loss either.

Poor Circulation causes baldness.


What Causes Hair Loss In Males?